The present invention relates to a fluidized bed filtering apparatus for purifying corrupt water (original water or water to be treated) in a sewer, a drain, a river, a lake, a marsh or the like.
A water treatment method called a contact oxidation method or a dipped filtering bed method is conventionally known for purifying corrupt water in a sewer, a drain, a river, a lake, a marsh or the like. There is a case that this kind of water treatment method is called a biological filtering method or a biological membrane filtering method because an oxidizing and decomposing process by a microorganism makes a great contribution to the purification in particular. In this water treatment method, a filtering chamber is filled with filtering material (contact material) made of a honeycomb tube, a nylon belt, a plastic formed filtering material, charcoal or activated coal, granular filtering material such as ceramics and sand. Corrupt water is passed through the filtering chamber to remove suspension substances (SS) and organic matters in original water.
In the above water treatment method, when the filtering operation continues, autogenous microorganisms in the original water propagates on the surface of the filtering material to form a membrane called a biological membrane, which promotes the removal of corrupt substances.
Filtering methods can be classified into a group of fixed bed and a group of fluidized bed. Filtration by a fluidized bed is performed with filtering material fluidized by the flow of original water. In general, granular filtering material the specific gravity of which is somewhat larger than that of water is used and the original water is passed upward to fluidize the filtering material. In contrast to the filtration with a fixed bed in which clogging is apt to occur near the inlet portion of filtering material in a short operation period because corrupt substances in original water is caught concentrically near the inlet portion, the filtration with a fluidized bed has an advantage that clogging is hard to occur because filtering material is always fluidized.
For instance, the Japanese Patent Unexamined Publication No. 3-38289 is a prior art of fluidized bed filtering apparatus.
In such a prior art fluidized bed filtering apparatus, however, because the outlet of a feed pipe for feeding water to be treated (corrupt water) to a filtering chamber is disposed in a filtering material layer, there is a case that particles of filtering material enter into the feed pipe when suspending the filtering operation, so that the feed pipe is clogged by the filtering material. When once the feed pipe is clogged, there is a case that the filtering material clogging the feed pipe becomes hard to be discharged only with the pressure by a feed water pump. Thus, the restart of the filtering operation becomes hard. It is a problem in the case of suspending the filtering operation for maintenance.
For resolving the above problem, there is another prior art of fluidized bed filtering apparatus in which a filtering material layer is support in the upper portion of a filtering chamber with a gravel layer, a porous plate and others to provide a space in the lower portion of the filtering chamber. The outlet of a feed pipe is disposed within the space. In this construction, filtering material does not enter into the feed pipe but clogging is apt to occur at the portion of the porous plate or the gravel layer because that portion acts as a fixed bed. A washing operation with an air scattering tube or the like provided within the space in the filtering chamber is required when clogging occurs. In this prior art, however, there is a defect that the frequency of the washing operation becomes high. Besides, in such a washing operation, microorganisms which propagated in the filtering material layer and make a great contribution to the purification are also washed away. Thus, a high frequency of washing operations brings upon a considerable decrease of the biological treatment effect.